CN103493406A - Optical transmitter and method for controlling the same - Google Patents

Abstract

Since it is difficult to emit a stable and reliable modulated lightwave signal by means of IQ modulators used for QAM format, a method for controlling an optical transmitter according to an exemplary aspect of the invention includes the steps of (a) keeping an optical amplitude of a continuous wave light output from the optical transmitter constant, (b) making operating point values in optical modulation converge to predetermined values during step (a), and (c) modulating the continuous wave light with multiple amplitudes and phase levels around the operating point values converged in step (b).

Description

Optical transmitting set and for controlling the method for this optical transmitting set

Technical field

The present invention relates generally to optical communication technique, particularly, relates to the optical communication technique of utilizing the multi-level modulation scheme.

Background technology

For the treatment of the demand day by day increased of the transmission of the information on optical fiber link and a kind of mode of optimizing the input in optical fiber link, be more effectively to use available bandwidth in a link so that increase its capacity.Wave division multiplexing (WDM) technology makes it possible to by the interpolation more reflector of different wave length and the number that receiver increases transfer channel.Yet, the characteristic in wdm system be subject to link inside amplifier bandwidth and depend on the active parts of link inside or the restriction of the wavelength of passive component.Therefore, the actual use of wdm system is restricted to S band (short band), C band (conventional belt) or the L band (long band) in spectrum.

The another kind of mode that increases the capacity of link is to increase spectrum efficiency (SE) by the information to transmitting with more effective modulation format.This can use in conjunction with WDM.Have up to the optical communication system of the transmission rate of 10Gb/s and mainly utilize the on-off keying (OOK) for modulation, wherein, information is encoded on two amplitude levels of lightwave signal.In addition, the Quadrature Phase Shift Keying (QPSK) that the information of higher capacity system based on on four phase place levels is encoded is utilized modulation scheme.Therefore, two binary bits of symbolic coding that can each transmission.This is at non-patent literature 1(NPL1) in describe.The necessary bandwidth of the needed spectrum of transmission information by this way, is used more effectively.

In order to the another kind of mode that increases even more spectrum efficiency in channel and therefore increase link capacity, be to use quadrature amplitude modulation (QAM), wherein, symbol is encoded on phase place and amplitude level, and is organized as the combination of the multistage amplitude in quadrature phase.At non-patent literature 2(NPL2) in the example of QAM system is disclosed.In NPL2, modulation format is 16QAM, and wherein, information is encoded into 16 grades, namely, and 4 binary bits of each symbol.With QPSK, compare, this makes it possible to increase spectrum efficiency.In addition, at non-patent literature 3(NPL3) in, the use to 512QAM is disclosed, wherein, information is encoded into 512 grades, that is, and 9 binary bits of each symbol, and compare with 16QAM, spectrum efficiency even increases manyly.Therefore, the QAM form is the effective means that increases link capacity.

As by as shown in NPL2 and NPL3, between attainable spectrum efficiency (SE) and attainable transmission range, exist compromise (trade off).Therefore, according to the distance on the optical fiber link with the signal be transmitted, advantageously can select the index of QAM form,, 2 power of the number of the number of the symbol of the modulation on constellation or the binary bits of in other words encoding on a symbol, should be compromise to optimize.The use that can send with the reflector of the light of different Q AM index modulation according to the setting of reflector is to optimize this compromise cost-effective mode.

The QAM form can utilize light IQ modulator to carry out, and this light IQ modulator is sometimes referred to as Descartes's modulator, vector modulator, double-parallel modulator or nested (nested) modulator according to source.In the IQ modulator, the signal of telecommunication drives can be called as sub-mach zhender (Mach-Zehnder) modulator (MZM) two independently mach zhender devices.Sub-MZM modulates phase place and the amplitude of identical light carrier.The phase place of one in its output relatively postponed 90 degree before being reconfigured.Phase delay between the output of sub-MZM can be called as orthogonal angles (angle of quadrature) and be 90 degree mould 180 degree ideally.These IQ modulators in NPL2 and NPL3 for the QAM form and modulate for QPSK at NPLl in addition.These IQ modulators provide effective and attested mode to carry out the QAM form.

Yet, be known that because there are the DC(direct current in the variation of temperature or aging the causing of device in the IQ modulator) and the drift of biasing.There is the affected biasing of three types, that is, and the DC of each in two sub-MZM biasing and setovering for the DC with the quadrature set angle.If use the modulator with same structure, known QPSK modulates and the QAM form.Drift in biasing causes setting improperly modulator, and this makes the degradation of the signal of transmission, and therefore makes the signal quality of reception reduce, or in the worst case, makes and can not be decoded to the signal received.This problem may be in production phase or the assembling stage of the reflector that uses modulator, in the characteristic test of modulator and whenever modulator namely starts or manifested during reset operation each during first for the modulation of data.Identical fault also likely occurs in the operating period of modulator.For OOK, phase shift keying (PSK) modulation and QPSK, these faults solve by using automatic bias to control (ABC) circuit, and this automatic bias control circuit is controlled the biasing of modulator and for compensating the DC offset change.By this way, the drift that the ABC technology can be when starting or resetting both and DC controls biasing during operation.

Non-patent literature 4(NPL4) disclose a kind of scheme, this scheme can be used in ABC with 90 degree phase places between the output of controlling the mach zhender device.This RF power spectrum based on minimizing modulation signal.Basic principle is, the interference enhancing RF power spectrum between I data component and Q data component, and therefore, orthogonal angles can be controlled by minimizing the RF power spectrum.The DC that this scheme makes it possible to control the IQ modulator in conjunction with the known method of the DC biasing for controlling sub-MZM setovers to carry out the QPSK modulation.

At patent documentation 1(PTL1) in, use the principle identical with the principle of NPL4, and in addition, add chattering frequency and control orthogonal angles with the spectrum component by controlling the supervision relevant to chattering frequency.In addition, also explained the ABC circuit based on shake for the control of the DC of mach zhender device biasing.In the mode with identical for NPL4, such method is effective for QPSK.Make it possible to compensation during operation and the biasing before the startup of the modulator of QPSK change.

Reference listing

Patent documentation

PTL1: Japanese Patent Application Laid-Open is announced No.2008-249848

Non-patent literature

The people's such as NPL1:L.Nelson " Capabilities of Real-Time DigitalCoherent Transceivers ", European Conference on Optical Communications (paper MolC5,2010).

The people's such as NPL2:P.Winzer " Generation and1,200-km Transmission of 448-Gb/s ETDM 56-Gbaud PDM 16-QAM using a Single I/Q Modulator ", (ECOC2010, PD2.2).

The people's such as NPL3:S.Okamoto " 512QAM (54Gbit/s) Coherent Optical Transmission over 150 km with an Optical Bandwidth of 4.1GHz ", (ECOC2010, PD2.3).

NPL4:R.A.Griffin?et?al.,"Integrated?DQPSK?Transmitters",(OFC2005,paper?OWE3).

Summary of the invention

Technical problem

A difference between QPSK form and QAM form is, QPSK is the phase-modulation with constant amplitude, and the QAM form is used a plurality of amplitudes and phase level.Therefore, local extremum occurs in the supervisory signal for controlling DC biasing in the mode such as the QAM form, and, for the QPSK form, do not have local minimum.Yet such ABC circuit can compensate the DC biasing occurred in the operating period of utilizing the QAM form and change, as long as modulator correctly is set in optimal conditions.Yet such ABC circuit can't be avoided the local extremum caused by the QAM form when starting or resetting, and therefore can't suitably and reliably set and setover.

Even in the situation that the use as shown in PTL1 utilizes the ABC technology of chattering frequency, can not avoid the appearance of the local extremum that causes due to the QAM form.

As mentioned above, the problem of the optical transmitting set that those are relevant is, because can not avoid in the startup of IQ modulator or the drift of the DC biasing in the IQ modulator while resetting, so be difficult to send the stable and problem of modulated light wave signal reliably by means of the IQ modulator for the QAM form.

Exemplary purpose of the present invention is to provide optical transmitting set and, for controlling the method for this optical transmitting set, this reflector and method can be sent by means of the IQ modulator for the QAM form stable and reliable modulated light wave signal.

Solution to problem

Comprise the steps: that according to the method for controlling optical transmitting set of illustrative aspects of the present invention (a) maintenance is constant from the light amplitude of the continuous glistening light of waves of optical transmitting set output; (b) will during step (a), make the operation point value in light modulation converge to predetermined value, and near the continuous wave light modulation that (c) will have a plurality of amplitude levels and a phase level is the operating point of restraining in step (b).

According to comprising of illustrative aspects optical transmitting set of the present invention: the laser of launching the continuous glistening light of waves; Modulate the optical modulator of the described continuous glistening light of waves; Control the automatic bias control circuit of magnitude of voltage of the direct current biasing of described optical modulator; The logic binary data is encoded and exported the encoder of multilevel signal; And amplify described multilevel signal and drive thus the driver of described optical modulator, wherein, make to keep constant from the light amplitude of the described continuous glistening light of waves of described optical modulator output, described automatic bias control circuit makes described magnitude of voltage converge to predetermined value, and described optical modulator utilize a plurality of amplitude levels and phase level by described continuous wave light modulation near the magnitude of voltage in convergence.

Technique effect

Exemplary advantage according to the present invention provides a kind of can send by means of the IQ modulator for the QAM form optical transmitting set stable and modulated light wave signal reliably and for controlling the method for this optical transmitting set.

The accompanying drawing explanation

Fig. 1 is the schematically showing of optical transmitting set that comprises the IQ modulator that utilizes the ABC circuit to be controlled.

Fig. 2 is the set of the analog result of the optical transmitting set for the QPSK form shown in Fig. 1.Fig. 2 A means the Line Chart of the output of band pass filter to the DC biasing.Fig. 2 B means the output of band pass filter and the Line Chart of the phase difference between the shake sinusoidal signal.Fig. 2 C means the Line Chart of the output of band pass filter to orthogonal angles.Fig. 2 D is the simulation eye pattern of QPSK lightwave signal.Fig. 2 E means the planisphere of the analog track of lightwave signal.Fig. 2 F means the planisphere of the tracing point of the sampling of the center at symbol shown in Fig. 2 E.

Fig. 3 is the set of the analog result of the optical transmitting set for the 64QAM form shown in Fig. 1.Fig. 3 A means the Line Chart of the output of band pass filter to the DC biasing.Fig. 3 B means the output of band pass filter and the Line Chart of the phase difference between the shake sinusoidal signal.Fig. 3 C means the Line Chart of the output of band pass filter to orthogonal angles.Fig. 3 D is the simulated light waveform of 64QAM lightwave signal.Fig. 3 E means the planisphere of the point of sampling in the center of the symbol in lightwave signal.Fig. 3 F means the Line Chart of amplitude of the output of the band pass filter in the I-MZM with the biasing that equals 0.Fig. 3 G means the Line Chart of the phase difference between the output of band pass filter and the reference sinusoidal signal in the I-MZM with the biasing that equals 0.Fig. 3 H means the Line Chart of amplitude of the output of the band pass filter in the Q-MZM with the biasing that equals twice Vpi.Fig. 3 I means the Line Chart of the phase difference between the output of band pass filter and the reference sinusoidal signal in the Q-MZM with the biasing that equals twice Vpi.Fig. 3 J means the Line Chart of the output of band pass filter to orthogonal angles.Fig. 3 K is the simulated light waveform of 64QAM lightwave signal when bias condition is different from ideal conditions.Fig. 3 L means the planisphere of the point of sampling in the center of the symbol in the 64QAM lightwave signal when bias condition is different from ideal conditions.Fig. 3 M is the planisphere with another local minimum in the 64QAM lightwave signal.

Fig. 4 is schematically showing according to the optical transmitting set of the first exemplary embodiment.

Fig. 5 illustrates the flow chart according to the method for the optical transmitting set of the first exemplary embodiment for control.

Fig. 6 is schematically showing according to the optical transmitting set of the second exemplary embodiment.

Fig. 7 is the flow chart for the method for controlling optical transmitting set illustrated according to the second exemplary embodiment.

Fig. 8 illustrates the flow chart according to the another kind of method of the optical transmitting set of the second exemplary embodiment for control.

Fig. 9 is schematically showing according to the optical transmitting set of the 3rd exemplary embodiment.

Figure 10 illustrates the flow chart according to the method for the optical transmitting set of the 3rd exemplary embodiment for control.

Figure 11 is by the planisphere on a polarization of the signal of the emission of the optical transmitting set according to the 3rd exemplary embodiment.

Embodiment

[the first exemplary embodiment]

Fig. 1 comprises that IQ modulator 110 and automatic bias control the schematically showing of optical transmitting set 1000 of (ABC) circuit 120.Optical transmitting set 1000 represented on Fig. 1 sends the lightwave signal 199 by 110 modulation of IQ modulator according to logic binary data stream 100.Encoder 101 generates the I component of IQ modulator 110 and the signal of Q component according to the modulation format of logic binary data stream 100 and optical transmitting set 1000.Two signals of telecommunication that generated by encoder 101 are amplified by driver 102 and 103, and it will be optimum making its amplitude for IQ modulator 110.Laser 104 is according to by driver 102 and the 103 driving signals that generate, sending continuous wave (CW) light by 110 modulation of IQ modulator.

IQ modulator 110 comprises two the sub-MZ Mach-Zehnders (MZM) 111 and 112 that are respectively used to I component and Q component.IQ modulator 110 also comprises phase-shifting element 113 and integrated supervision photodetector (PD) 114.Alternatively, monitor that PD114 can be independent of IQ modulator 110 and be set, and receive the tap part (tapped portion) of the output light-wave signal of IQ modulator.Phase-shifts element 113 makes it possible to control the angle of the quadrature in IQ modulator 110.Monitor that PD114 generates and the proportional signal of telecommunication of the proportional intensity of light signal of modulating, and can be used in the situation that monitors IQ modulator 110.

ABC circuit 120 is controlled the DC biasing of sub-MZM111 and 112 and the biasing of controlling orthogonal angles by phase-shifting element 113 according to the supervisory signal provided by supervision PD114.ABC circuit 120 use are by with corresponding independent frequency f1, f2 and f3, generating the oscillator 131,132 of sinusoidal signal and the biasing that MZM111, MZM112 and phase-shifting element 113 are controlled respectively in 133 shakes that generated.These frequencies can be in the scope from several KHz to several megahertzes.Amplified by amplifier 121 by the supervisory signal that monitors the PD114 generation, and be divided into three equal signals by frequency divider 122 subsequently.

Control circuit 140 generates the DC biasing of I-MZM111 according to the sinusoidal voltage of the output of frequency divider 122 and the frequency f 1 that generated by oscillator 131.Band pass filter 141 has centre frequency f1 and narrow the bandwidth that is enough to get rid of other frequency component of f2 and f3.The amplitude of the output of band pass filter 141 is proportional with the frequency component at the f1 place of the supervisory signal generated by supervision PD114.Phase comparator 142 generate proportional with the amplitude of the output of band pass filter 141 and and by band pass filter 141, extracted near signal f1 with by the proportional error signal of phase difference between the sinusoidal signal at the f1 place of oscillator 131 generations.Biasing circuit 143 generates DC voltages with the biasing of controlling I-MZM111 so that minimize that generate by phase comparator 142 and have an error signal at the jittering component at frequency f 1 place.

Another control circuit 150 is identical with control circuit 140, and has the band pass filter of centre frequency f2.Control circuit 150, in the mode identical with control circuit 140, is controlled the DC biasing of Q-MZM112 according to the output to by monitoring the proportional frequency divider 122 of supervisory signal that PD114 generates.

The 3rd output of frequency divider 122 is fed to envelope detector 160, and the output of this envelope detector 160 is carried out filtering by the band pass filter 161 with centre frequency f3.The output of envelope detector 160 generates the signal of reflection by the RF power spectrum that monitors the supervisory signal that PD114 generates.Lock-in circuit 162 use chattering frequency f3 generate and the proportional error signal of the output of band pass filter 161.Finally, angle biasing circuit 163 generates and minimizes and voltage that have the error signal of chattering frequency f3 that generate by lock-in circuit 162.The voltage generated by angle biasing circuit 163 is controlled the orthogonal angles of IQ modulator 110 by phase-shifting element 113.

At first, explain the analog result of QPSK form.Fig. 2 is the set of analog result of the optical transmitting set 1000 of the form of the QPSK for the baud rate with 32Gbaud shown in Fig. 1.The bandwidth that monitors PD114 is 1GHz.Frequency f 1, f2 and f3 are set to respectively 4MHz, 9MHz and 7.5MHz.Correspondingly design band pass filter 141,161 and be included in the band pass filter in control circuit 150.The peak to peak amplitude that is there is twice Vpi by each driving signal of driver 102 and 103 outputs.Vpi is illustrated in the situation that there is no modulation in the maximum transmitted condition of sub-MZM111 and 112 and the difference in the voltage between the minimum transfer condition.The analogue value of Vpi equals 3V.This drive condition is desirable for the QPSK modulation.

Fig. 2 A means the Line Chart of the output of band pass filter 141 to the biasing of the DC by the normalized sub-MZM111 of Vpi.There is minimum value in the maximum transmitted characteristic that means MZM111 and each some place of minimum transfer characteristic.Fig. 2 B mean the output of band pass filter 141 and the shake sinusoidal signal that generated by oscillator 131 between the Line Chart of phase difference.This phase place replaces at each minimum point place of the curve shown in Fig. 2 A.

Then, explain the example of the DC biasing of controlling MZM111.In the startup of optical transmitting set 1000 or while resetting, can consider the different condition of normalized biasing.According to temperature and the state of device, the easily translation on its abscissa of the voltage characteristic of the modulator shown in Fig. 2 A and Fig. 2 B.Yet, for the facility of conventional reason and research, we are thought of as characteristic fixing, and make the contrary amount of voltage translation.Therefore, due to this custom and consider the periodicity of the characteristic of modulator, any one in may getting the value between 0V and 2V of the normalized voltage when starting or resetting.When this value is between 0V and 0.5V the time, immediate minimum value is 0V.Yet, due to the signal monitored with reference to the sinusoidal signal homophase, so to continue be strict positive (strictly positive) to the error signal generated by phase comparator 142, and the biasing generated by biasing circuit 143 continues to increase away from 0V.

Voltage process 0.5V and increase are until reach 1V.In this case, can reach a minimum value.In addition, when when the 1V, signal and with reference to sinusoidal signal by anti-phase, therefore, the error signal generated by biasing circuit 143 will diminish.As a result, the deviation generated by biasing circuit 143 will be maintained at 1V.Correspondingly, due to phase relation, the 1V(biasing equals Vpi) be stable minimum value, and 0V is unsettled.According to identical mechanism, ABC circuit 120 generates the biasing of 1V.In the same way, when change in voltage that the change of following the tracks of due to the temperature of operating period causes, the normalization biasing of generation is maintained at 1V.This means that MZM111 is biased at the Vpi place, this is best bias condition for QPSK.Identical with operation mentioned above for the operation of biasing of controlling MZM112.

Fig. 2 C means that the output of band pass filter 161 is to the Line Chart from 0 ° to 360 ℃ of orthogonal angles of being controlled by phase-shifting element 113.Signal reaches minimum value at each some place of the orthogonality that obtains orthogonal angles, and namely, orthogonal angles is 90 degree mould 180 degree.This is because the signal on I component and the interference between the signal on the Q component minimum fact under this configuration causes.Lock-in circuit 162 is controlled the biasing generated by angle biasing circuit 163, so that minimize the output of band pass filter 161.Under this configuration, for QPSK, orthogonal angles is optimized in modulation.

Regardless of condition, the characteristic of Fig. 2 A, Fig. 2 B and Fig. 2 C is all identical with three biasings of the IQ modulator 110 of being controlled by ABC circuit 120.This means that ABC circuit 120 can find the optimal conditions for the QPSK modulation when starting or resetting.And, for the variation of the biasing of operating period of the optical transmitting set 1000 shown in Fig. 1, ABC circuit 120 can compensate these to be changed, and the biasing of IQ modulator 110 is remained under its optimal conditions.

Fig. 2 D is the simulation eye pattern that sends under the condition that 32Gbaud QPSK signal and IQ modulator 110 controlled by ABC circuit 120 the QPSK lightwave signal 199 that optical transmitting set 1000 as shown in Figure 1 generates at optical transmitting set 1000 with optimum biasing.

Fig. 2 E means the planisphere of the analog track of lightwave signal 199.Fig. 2 F means the planisphere of the tracing point of the sampling of the center at symbol shown in Fig. 2 E.Four possible symbols of QPSK modulation are correctly positioned and separate.ABC circuit 120 makes it possible to when starting or resetting and control during operation IQ modulator 110 under optimal conditions.

Next, the analog result of description below QAM form.Fig. 3 is the set of analog result of the optical transmitting set 1000 of the modulation format for the 64QAM that is chosen as the baud rate with 32Gbaud shown in Fig. 1.The chattering frequency of IQ modulator 110 and ABC circuit 120 is selected as identical with those of the QPSK form shown in Fig. 2.Yet encoder 101 comprises two digital to analog converters (DAC).DAC is transformed into logic binary data stream 100 signal of telecommunication with 8 levels.The multistage signal of telecommunication is amplified by driver 102 and 103, and the multiple drive power signal is fed to IQ modulator 110 to modulate CW light according to 64QAM.The peak to peak amplitude that is there is twice Vpi by the driving signal of driver 102 and 103 outputs.This drive condition is desirable for the 64QAM form that has suitable difference between different levels.

Fig. 3 A means the Line Chart of the output of band pass filter 141 to the biasing of the DC by the normalized sub-MZM111 of Vpi.Condition for this simulation is that the DC biasing of Q side is Vpi, and orthogonal angles is 90 degree.Fig. 3 B mean the output of band pass filter 141 and the shake sinusoidal signal that generated by oscillator 131 between the Line Chart of phase difference.Fig. 3 C means the Line Chart of the output of band pass filter 161 when the DC biasing is set to the Vpi on I and the sub-MZM of Q to orthogonal angles.Those shown in these results and Fig. 2 come to the same thing, and if the DC biasing ABC that shows the Q side is set to Vpi and orthogonal angles is set to 90 degree, and ABC circuit 120 can be controlled at DC near Vpi.

Fig. 3 D is the simulated light waveform of 64QAM lightwave signal 199 while under the ideal conditions at ABC circuit 120, setting the IQ modulator.Fig. 3 E means the planisphere of the point of sampling in the center of the symbol in lightwave signal 199 under identical condition.As shown in Fig. 3 E, there are 64 different possible symbols, it is equally spaced and be positioned on the grid of 8X8.If these results show the operating period that DC is biased in the IQ modulator and approach ideal conditions, ABC circuit 120 can be controlled IQ modulator 110 according to the 64QAM form and drives.

Yet, compare the fact that no longer there is uniform amplitude with QPSK due to the QAM form, when bias condition is different from ideal conditions, other minimum value on supervisory signal occurs.This situation may occur in the startup of optical transmitting set or while resetting.

In these conditions that the explained later local minimum occurs one.This condition is, the biasing of I-MZM equals 0V, and the biasing of Q-MZM equals twice Vpi, and orthogonal angles equals 45 degree, and changes near being biased in these points.Fig. 3 F means the Line Chart of amplitude of the output of band pass filter 141.Fig. 3 G means the output of band pass filter 141 and by the Line Chart of the phase difference between the reference sinusoidal signal of oscillator 131 output.As shown in Fig. 3 F, the amplitude of supervisory signal is equaling to have minimum value under the bias condition of 0V.According to the phase place on this aspect, change, this is the stable condition for the ABC circuit.

In the same way, Fig. 3 H means the Line Chart of the amplitude of the output that is included in the band pass filter in another control circuit 150.Fig. 3 I means the Line Chart of the phase difference between the output of band pass filter and the reference sinusoidal signal that generated by oscillator.In this case, as shown in Fig. 3 H, amplitude has under the bias condition that equals twice Vpi and has minimum value.It is stable condition that phase change at that point shows it for the ABC circuit.Finally, Fig. 3 J means the Line Chart of the output of band pass filter 161 to orthogonal angles.In this case, because the angle of 45 ° is the minimum value of characteristic, the angle of 45 ° is stable condition.Therefore, due to the QAM form, in the biasing of I-MZM, equal 0V, the biasing of Q-MZM equals 2Vpi, and orthogonal angles equals in the situation of 45 °, and the local minimum of supervisory signal occurs.

Fig. 3 K is the simulated light waveform of the 64QAM lightwave signal 199 in being different from these bias conditions of ideal conditions.Fig. 3 L means the planisphere of the point of sampling in the center of the symbol in 64QAM lightwave signal 199 under identical condition.Clearly, because some symbols are demoted and these symbols can not be by correct demodulation, so can not correctly carry out the 64QAM form under these conditions.Therefore, start near these biasings at optical transmitting set or while resetting, because heat condition and modulator state cause the ABC circuit to make setovering converging on this local minimum, and will can correctly not carry out modulation.

The existence of local minimum is not limited to these conditions.Fig. 3 M is that the biasing at I-MZM equals 0.5Vpi, and the biasing of Q-MZM equals the planisphere that has another local minimum in situation that 0.2Vpi and orthogonal angles equal 45 °.And the existence of these minimum values is not limited to the 64QAM form.Comprise that for having amplitude level is the QAM form of the different index of a plurality of 16QAM, 32QAM, 128QAM, 256QAM and 512QAM, exists other local minimum.

Next, explain the optical transmitting set according to the present embodiment.Fig. 4 is schematically showing according to the optical transmitting set of the present embodiment.Optical transmitting set 400 sends the lightwave signal 499 of modulating according to logic binary data stream 498 with the modulation format of reflector.Optical transmitting set 400 can be to send the xQAM reflector with the lightwave signal 499 of xQAM form modulation according to logic binary data stream 498.Here, x means the QAM index, for example for 64QAM form x, equals 64.Laser 404 sends continuous wave (CW) light by IQ modulator 410 modulation as optical modulator.IQ modulator 410 can be identical with the IQ modulator 110 shown in Fig. 1.According to the output of the integrated supervision PD in IQ modulator 410, automatic bias is controlled three DC biasings that (ABC) circuit 420 is controlled IQ modulator 410,, controls the DC biasing of the sub-MZM of I, the DC biasing of controlling the DC biasing of the sub-MZM of Q and controlling orthogonal angles that is.Encoder 401 comprises data encoder unit 405 and digital to analog converter (DAC) 406,407.Data encoder unit 405 is divided into logic binary data stream 498 two subflows that are encoded to the multilevel signal that generates DAC406 and 407.DAC406 and 407 output are amplified by corresponding driver 402 and 403, to generate the corresponding I that drives in IQ modulator 410 and the signal of telecommunication of the sub-MZM of Q.

Optical transmitting set 400 comprises the driver controller 470 that comprises timer 471 and switch element 472.Timer 471 comes control switch unit 472 according to predetermined time Tswitch.Time T switch measured or alternatively starts to measure from the resetting time of optical transmitting set 400 since start-up time, and was designed to make ABC circuit 420 to keep time enough to reach convergence.Switch element 472 guarantees, driver 402 and 403 startups at optical transmitting set 400 or be disconnected while resetting.When timer 471 has been measured time T switch, activator switch unit 472, and then switch element 472 is connected driver 402 and 403.

Next, explain for controlling the method according to the optical transmitting set of the present embodiment.Fig. 5 is the flow chart illustrated for the method for the optical transmitting set 400 shown in control chart 4.Hereinafter, explain the example of the operation of optical transmitting set 400 with reference to Fig. 5.In the present embodiment, there is the 132Gb/s reflector of 64QAM form as optical transmitting set 400.Therefore, this reflector is operated under 22Gbaud.Logic binary data stream 498 is the binary data streams with aggregate rate of 132Gb/s.Each in the output of data encoder 405 has the aggregate rate of 66Gb/s.DAC406 and 407 generates 8 grades of signals of telecommunication with 22Gbaud.

At first optical transmitting set 400 was switched on when starting, and its initiating sequence starts.Switch element 472 keeps driver 402 and 403 to disconnect (the step S401 of Fig. 5), namely, keeps the output voltage values of driver constant.As a result, the light amplitude of the glistening light of waves has been held constant continuously.In this, ABC circuit 420 and laser 404 and IQ modulator 410 are connected.Yet, because driver 402 and 403 remains open, so its output is zero.Under this condition, ABC circuit 420 is controlled the DC biasing of IQ modulator 410.As mentioned above, when the startup of IQ modulator 410, because local minimum occurs causing its DC biasing to be set mistakenly with the 64QAM form.Yet, because modulating data is zero, namely, constant, so ABC circuit 420 can be so that the DC of sub-MZM biasing converges to its minimum transfer point Vpi, this minimum transfer point Vpi is the magnitude of voltage with the direct current biasing of the Optimum Operation point value of IQ modulator 410, and is also the optimum setting point of 64QAM.The Optimum Operation DC biasing of sub-I and QMZM equals Vpi, mould 2*Vpi, and this Optimum Operation DC biasing is to set the biasing of mach zhender interferometer for destructive interference.For the optimum operating point of biasing of controlling the orthogonal angles between I and Q MZM, be the voltage corresponding with the phase difference with 90 degree moulds 180 degree.

Timer 471 is measured and is started institute's elapsed time from the start-up time of optical transmitting set 400, and whether definite institute elapsed time has reached Tswitch(step S402).In time T switch(step, S402/ is) to locate, ABC circuit 420 has been restrained the DC biasing.Timer 471 sends the signal that arrives Tswith to switch element 472.Then, switch element 472 is connected driver 402 and 403(step S403).Now, IQ modulator 410 starts according to 64QAM form light modulated.Because the DC of sub-MZM biasing has arrived its optimum point, ABC circuit 420 can be followed the trail of the drift of DC biasing during operation.In addition, under this condition, ABC circuit 420 can also control to orthogonal angles the best setting (step S404) of its 90 degree in the situation that do not run into any local minimum.By this way, the initiating sequence of optical transmitting set 400 completes, and for QAM, modulates the DC biasing of correctly having set IQ modulator 410.As a result, in the operating period of optical transmitting set 400, ABC circuit 420 can be followed the trail of any variation in the DC biasing.

Alternatively, the sequence of Fig. 5 can be applied in when the resetting of reflector 400.In that case, the homing sequence of optical transmitting set 400 completes, and has correctly set the DC biasing of IQ modulator 410.As a result, in the operating period of optical transmitting set 400, ABC circuit 420 can be followed the trail of any variation in the DC biasing.

In the alternate embodiments of the present embodiment, can set by setting data encoder 405 suitably the index of the QAM form of the optical transmitting set 400 shown in Fig. 4.For example, can select 256QAM for the form of modulation when starting.In this embodiment, according to the flow chart shown in Fig. 5, for optical transmitting set 400, can be independent of selected modulation format and correctly start and operate.

As mentioned above, according to the present embodiment, optical transmitting set can send by means of the IQ modulator for the QAM form lightwave signal stable and that modulate reliably.This is because, by use constant or acyclic homologically trioial data processed when starting, the DC biasing of IQ modulator can converge to its minimum transfer point.In other words, make it possible to avoid reach the local minimum of the supervisory signal of the ABC circuit for thering is the QAM form.Therefore, the present embodiment makes it possible to realize the correct of modulation and starts reliably.In addition, once initiating sequence is implemented, the control of being undertaken by the ABC circuit makes it possible to realize correct operation.And, needn't use and may any other light disturbed occur with the light wave carrier wave.Finally, the present embodiment can be for QAM form and the QPSK form with any index.

In addition, it is possible by means of simple ready-made electronic equipment, implementing according to the optical transmitting set of the present embodiment, and therefore, it is that to have a cost effective.In addition, can implement optical transmitting set with little encapsulation (footprint), therefore can be made less.

[the second exemplary embodiment]

Fig. 6 is schematically showing according to the optical transmitting set of the second exemplary embodiment.Optical transmitting set 600 is to send the xQAM reflector with the lightwave signal 699 of xQAM form modulation according to logic binary data stream 698.Here, x means the QAM index.Encoder 601 is identical with the encoder 401 shown in Fig. 4.Encoder 601 comprises data encoder and two DAC, and generates the multistage signal of telecommunication after being amplified by driver 602 and 603, to drive IQ modulator 610.IQ modulator 610 drives signal to modulate the CW light sent by laser 604 according to I and Q.Driver 602 and 603 can be disconnected by switch element 672.Switch element 672 command-driven devices 602 and 603 supply voltages.Switch element 672 is controlled by control unit 630.Control unit 630 is by the electric circuit constitute, and can comprise microprocessor.

Three DC biasings of IQ modulator 610 are controlled by ABC circuit 620.The output that is integrated in the supervision PD in IQ modulator 610 is cut apart by frequency divider 674.An output of frequency divider 674 is used to control the DC biasing of IQ modulator 610 by ABC circuit 620.Another output of frequency divider 674 is that the value of controlling the DC biasing of the orthogonal angles in IQ modulator 610 is carried out record by angle analysis device 673 reference settings.Angle analysis device 673 is controlled by control unit 630.In addition, angle analysis device 673 will be for the optimal DC voltage of the controlling orthogonal angles ABC circuit 620 of communicating by letter.If ABC circuit 602 is similar to the ABC circuit 120 shown in Fig. 1, the suitable information about the biasing for controlling orthogonal angles is provided by the angle analysis device 673 that is similar to angle biasing circuit 163.

Scanning circuit 675 generates different DC voltages and is controlled by control unit 630.The output of scanning circuit 675 is connected to angle analysis device 673.The output of angle analysis device 673 writing scan circuit 675 in the output that receives frequency divider 674, the output of frequency divider 674 is signals that the supervision PD from IQ modulator 610 is cut apart.The output of scanning circuit 675 is also connected to switch 676.Switch 676 can be chosen as its output the voltage generated by scanning circuit 675 or the DC biasing generated by ABC circuit 620, so that control the orthogonal angles in IQ modulator 610.Switch 676 is also controlled by control unit 630.Control unit 630 can also switch on and off ABC circuit 620, and monitors the rub-out signal for the control generation of DC biasing by ABC circuit 620.Here, error signal is defined as the proportional signal of difference between its size and phase place and actual reception value and standard value.

Fig. 7 illustrates the flow chart according to the method for the optical transmitting set 600 of the present embodiment for control.Sequence shown in Fig. 7 makes it possible to realize the correct startup of the xQAM reflector shown in Fig. 6.When optical transmitting set 600 is energized or is reset, control unit 630 command switch unit 672 make driver 602 and 603 disconnect (step S601 in Fig. 7) by the power supply of Down Drive 602 and 603.In the same way, control unit 630 is closed the power supply (step S602) of ABC circuit 620.Control unit 630 sets switch 676 for selecting the output (step S603) of scanning circuit 675.

Then, control unit 630 command scan(ning) circuit 675 are taken at each in N+1 magnitude of voltage VQ in suitable voltage range Vqad.For the orthogonal angles in IQ modulator 610, suitable voltage range Vqad can be selected as making it can produce 180 degree phase differences.The number of these magnitudes of voltage can be approximately 5.For each in the VQ value, angle analysis device 673 is with low speed analog to digital converter (ADC) record value VQ and be included in the level Vmon of the correspondence of the supervision PD in IQ modulator 610.These values can be recorded in (step S604) on the volatile memory be included in angle analysis device 673.Then, the Vmon value of control unit 630 order angle analysis device 673 sweep records, and search maximum and minimum value (step S605).The average voltage VHalf(step S606 that angle analysis device 673 generates as the mean value of the voltage VQ corresponding with maximum Vmon and minimum Vmon).This average voltage is set as the approximately needed DC biasing of 90 degree corresponding to the orthogonal angles by IQ modulator 610 haply.90 degree are that the estimation of the constructive interference from IQ modulator (0 ° of quadrature) starts and to half of the destructive interference in IQ modulator (180 spend quadrature).Control unit 630 reads VHalf and sets VHalf(step S607 for scanning circuit 675).

Then, control unit 630 is set as ABC circuit 620 to connect (step S608), and command switch unit 672 makes driver 602 and 603 connect (step S609).ABC circuit 620 is controlled the DC biasing of I and the sub-MZM of Q of IQ modulator 610, and the orthogonal angles in IQ modulator 610 is maintained at about 90 degree.In this configuration, ABC circuit 620 can find the suitable DC biasing that does not fall into the incorrect local minimum caused due to the QAM form for sub-MZM.

The rub-out signal of the DC biasing of 630 couples of sub-MZM of ABC circuit 620 poll of control unit.If ABC circuit 620 is similar to the ABC circuit 120 shown in Fig. 1, the rub-out signal of poll is signal corresponding in the output of phase comparator 142 and control circuit 150.Control unit 630 determines whether the rub-out signal of DC biasing restrains (step S610).When rub-out signal by considering whether the DC biasing has restrained the threshold value of selecting when following (step S610/ is), and control unit 630 DCs of order ABC circuit 620 using VHalf as the orthogonal angles of controlling IQ modulator 610 setover to apply (step S611).If ABC circuit 620 is similar to the ABC circuit 120 shown in Fig. 1, the output of angle biasing circuit 163 is set to VHalf.Then, control unit 630 command switches 676 are selected the DC biasing (step S612) of the orthogonal angles for controlling ABC circuit 620.In this configuration, ABC circuit 620 can be controlled the orthogonal angles in IQ modulator 610 effectively, and is about 90 degree by this angle initialization, guarantees not exist the generation (step S613) of the local minimum that any discomfort that causes due to the QMA form works as.

Once realize the initiating sequence of optical transmitting set 600, the DC biasing of IQ modulator 610 is just correctly set.In the operating period of optical transmitting set 600, the ABC circuit can be followed the trail of all offset change.

In the alternate embodiments of the present embodiment, VHalf is applied to the moment of ABC circuit 620 and can be determined by the timer that is similar to the timer 471 shown in Fig. 4, rather than determines by the rub-out signal of poll ABC circuit 620.

Fig. 8 illustrates the flow chart according to the another kind of method of the optical transmitting set 600 of the present embodiment for control.Sequence shown in Fig. 8 makes it possible to realize the correct startup of the xQAM reflector shown in Fig. 6.When optical transmitting set 600 is energized or is reset, step S621 in control unit 630 command switch unit 672 Down Drives 602 and 603(Fig. 8).Control unit 630 is closed the power supply (step S622) of ABC circuit 620.Control unit 630 is set as switch 676 to select the output (step S623) of scanning circuit 675.

Then, control unit 630 command scan(ning) circuit 675 are taken at each in N+1 magnitude of voltage VQ in suitable voltage range Vqad.For each in the VQ value, angle analysis device 673 record value VQ and be included in the level Vmon of the correspondence of the supervision PD in IQ modulator 610.These values can be recorded in (step S624) on the volatile memory be included in angle analysis device 673.Then, Vmon value and search maximum and the minimum value (step S625) of control unit 630 order angle analysis device 673 sweep records.The voltage VHalf(step S626 that angle analysis device 673 generates as the mean value of the voltage VQ corresponding to maximum Vmon and minimum Vmon).This voltage is set as the approximately required DC biasing of 90 degree corresponding to the orthogonal angles by IQ modulator 610 haply.Control unit 630 reads VHalf and is scanning circuit 675 setting VHalf(step S627).

Then, control unit 630 is set ABC circuit 620 for connection (step S628).ABC circuit 620 is controlled the DC biasing of I and the sub-MZM of Q of IQ modulator 610, and the amplitude of modulation signal still is retained as constant or zero, because driver 602 and 603 is de-energized.In this configuration, ABC circuit 620 can find the suitable DC biasing that does not fall into the incorrect local minimum caused due to the QAM form for sub-MZM.

The rub-out signal of the DC biasing of 630 couples of sub-MZM of ABC circuit 620 poll of control unit.Control unit 630 determines that whether the rub-out signal of DC biasing is by convergence (step S629).When rub-out signal is whether restrained the threshold value of selecting by consideration DC biasing below (step S629/ is), control unit 630 DCs of order ABC circuit 620 using VHalf as the orthogonal angles of controlling IQ modulator 610 setover to apply (step S630).Then, control unit 630 command switches 676 are selected the DC biasing (step S631) of the orthogonal angles for controlling ABC circuit 620.In that configuration, ABC circuit 620 can effectively be controlled orthogonal angles in IQ modulator 610 and be about 90 degree by this angle initialization, guarantees not exist the generation (step S632) of any unsuitable local minimum caused due to the QMA form.

Then, control unit 630 command switch unit 672 make driver 602 and 603 energisings (step S633).As a result, IQ modulator 610 is in fact with xQAM form modulated light wave carrier.In this case, similarly, once the initiating sequence of optical transmitting set 600 is implemented, the DC biasing of IQ modulator 610 is just correctly set.In the operating period of optical transmitting set 600, the ABC circuit can be followed the trail of all offset change.

[the 3rd exemplary embodiment]

Fig. 9 is schematically showing according to the optical transmitting set of the 3rd exemplary embodiment.Optical transmitting set 900 is to launch the multiplexed xQAM reflector of polarization with the light wave 999 of xQAM form modulation according to logic binary data stream 998.Herein, x means the QAM index.Optical transmitting set 900 comprises recording controller 970, and this recording controller 970 comprises timer 971, data switch 972 and training mode maker 973.

Logic binary data stream 998 is through data switch 972.Data switch 972 is according to its State-output logic binary data stream 998 or the fixing data sequence that generated by training mode maker 973.Data switch 972 receives order from timer 971.The selected lightwave signal 999 of corresponding modulation that makes of data pattern by training mode maker 973 emission has three or four possible states, between these three or four possible states state adjacent at them, have respectively 90 degree phase difference and there is uniform amplitude in the center of their symbols.

The output of data switch 972 is by encoder 901 codings, and this encoder 901 generates four multilevel signals in order to modulate described output with the xQAM form.Encoder 901 comprises data encoder 905, and this data encoder 905 generates four streams, and these four streams convert multilevel signal to by four DAC906,907,908 and 909.The output of DAC is amplified by corresponding driver 902,903,904 and 905.

CW light is by laser 904 emission and maintain coupler (CPL) 913 by polarization and cut apart.1 output of coupler 913 is fed in the IQ modulator 911 of the IQ modulator 110 be similar to shown in Fig. 1.Another output of coupler 913 is fed in another IQ modulator 912 of the IQ modulator 911 shown in being similar to.IQ modulator 911 and 912 output are by optical polarization beam combiner (PBC) 914 combinations, and the moving beam combiner 914 of this polarization makes the polarization of 90 degree in its output.IQ modulator 911,912, coupler 913 and optical polarization beam combiner 914 can be integrated in the single package as single dual polarization (DP) IQ modulator 910.

CW light is modulated according to the driving signals by driver 902 and 903 generations by IQ modulator 911 on the X polarization.On the Y polarization is moving, CW light is modulated according to the driving signals by driver 904 and 905 generations by another IQ modulator 912.The DC biasing of IQ modulator 911 is subject to the control of ABC circuit 921, and the DC of another IQ modulator 912 biasing is subject to the control of ABC circuit 922.These ABC circuit 921 and 922 can be integrated into the single ABC circuit 920 of the DC biasing of controlling IQ modulator 910.

Figure 10 illustrates the flow chart according to the method for the optical transmitting set 900 of the present embodiment for control.The sequence of the flow chart shown in Figure 10 makes it possible to realize the correct startup of the PM-xQAM reflector 900 shown in Fig. 9.When optical transmitting set 900 is energized or is reset, data switch 972 is set to the training mode (step S901 in Figure 10) of output by 973 emissions of training mode maker.Timer 970 is similar to the timer 471 shown in Fig. 4.Timer 971 is measured and is started institute's elapsed time from the start-up time of optical transmitting set 900, and whether definite institute elapsed time has reached Tswitch(step S902), wherein Tswitch is designed such that ABC circuit 920 had arrived stable state before Tswitch.In time T switch(step, S902/ is) afterwards, data switch 972 its output of switching and output logic binary data stream 998(step S903).Character according to the training mode by 973 emissions of training mode maker, in training mode, guarantee under the absent variable condition of the local minimum caused due to the xQAM form, ABC circuit 920 can correctly be controlled all DC biasings of DP-IQ modulator 911,912 when starting.At that time, optical transmitting set 900 emission xQAM data and DC biasing, its IQ modulator has been set to correct value when starting.In addition, the ABC circuit can be followed the trail of the variation in the DC biasing occurred during operation.

Figure 11 is the planisphere on the polarization of signal of optical transmitting set as shown in Figure 9 900 emissions.Modulation format is 16QAM.Exist 16 kinds equidistant and be distributed in the possible state on the 4X4 grid.On each symbol, 4 corresponding bit sequences mean a kind of situation of Gray code.When encoder 901 generates multilevel signal according to this coding, the utilizing emitted light symbol on a constellation is observed the constellation shown in Figure 11.In this case, by selecting only equidistant with origin (origin) symbol, can design the training mode generated by training mode maker 973.Namely, symbol for example corresponding to " 1011 " (A), " 0011 " (B), " 1111 " (C) and " 0111 " sequence (D).Can use the combination in any of at least three in these four symbols.For instance, can use binary system PRBS(pseudorandom bit stream) repetition of 11 patterns, sequence " 00 " is encoded as (A), and " 01 " is encoded as (B), and " 11 " are encoded as (C), and " 10 " are encoded as (D).

Can change the index of the QAM form of optical transmitting set 900.In this case, each index that can set that training mode maker 973 is the QAM form keeps the setting of training mode and launches corresponding training mode.In addition, optical transmitting set 900 can be launched the light wave with the modulation of QPSK form.Therefore, for any modulation format that can be employed, optical transmitting set 900 correctly is set as its DC and is setovered when starting.In addition, the operation that makes optical transmitting set 900 is best, although produce offset drift in its operating period.

In the operating period of optical transmitting set, once the DC biasing has arrived their Best Point, the ABC circuit just can be followed the trail of the drift of DC biasing basically.Yet, in alternative example, the aging value that floats to the physical restriction of the voltage that can generate close to the ABC circuit caused in the DC biasing of modulator.Although the ABC circuit can compensate the drift in the biasing scope, but it can generate the DC biasing, and this may be favourable, in order to make the life-span of reflector longer, so that reflector resets, make the ABC circuit converge to the minimum DC biasing corresponding to the optimum operation value of IQ modulator.The existence prevention DC of the local minimum caused by the QAM modulation in this case, converges to best DC bias after being biased in and resetting.

In order to solve this technical problem, advantageously when reflector operates, the output voltage values of driver is changed to fixed value, and the maintenance output voltage values is constant.As an example, when reflector operates, the solution that is described to above first, second, and third embodiment is applicable.After the DC biasing converges to Best Point, driver starts normal running.Namely, driver starts amplify the signal of telecommunication generated by encoder and the signal of telecommunication of amplification is applied to sub-MZM.

According to this example, in reflector operating period, after the resetting of ABC circuit, the DC biasing of IQ modulator can converge to optimal point of operation again.

Although with reference to exemplary embodiment of the present invention, illustrate especially and described the present invention, the present invention is not limited to these embodiment.To be understood that by those skilled in the art, in the situation that do not break away from the spirit and scope of the present invention that are defined by the claims, can on form of the present invention and details, make various modifications.

Industrial applicibility

The present invention can be applied to the optical communication system of utilizing the multi-level modulation scheme.

Reference numerals list

400,600,900 optical transmitting sets

401,601,901 encoders

402,403,602,603,902,903,904,905 drivers

404,604,904 lasers

410,610,911,912IQ modulator

420,620,920ABC circuit

470 driver controllers

630 control units

970 recording controllers

Claims (10)

1. one kind for controlling the method for optical transmitting set, and described method comprises the steps:

(a) light amplitude of the continuous glistening light of waves during the maintenance light modulation is constant;

(b) the operation point value in will the described light modulation during step (a) converges to predetermined value; And

(c) near to utilize a plurality of amplitude levels and phase level be the described operation point value of restraining in step (b) by described continuous wave light modulation.

2. according to claim 1 for controlling the method for optical transmitting set, wherein,

In step (a), will keep constant for the output voltage values of the driver of light modulation;

In step (b), will converge to predetermined magnitude of voltage with the magnitude of voltage of the direct current biasing of the described operation point value of optical modulator; And

In step (c), by described continuous wave light modulation, be near the magnitude of voltage of the convergence of the direct current biasing of described optical modulator.

3. according to claim 2 for controlling the method for optical transmitting set, wherein,

In step (a), described driver is held to disconnect and the output zero voltage value reaches the scheduled time;

In step (b), within described predetermined time, by means of the automatic bias control method, the magnitude of voltage of described direct current biasing is converged to the minimum transfer point of described optical modulator; And

In step (c), connect described driver, and described optical modulator is modulated the described continuous glistening light of waves according to the quadrature amplitude modulation form.

4. according to claim 1 for controlling the method for optical transmitting set, wherein,

In step (a), will keep constant for the output voltage values of the driver of light modulation;

In step (b), restrain the rub-out signal of the direct current biasing corresponding with the described operation point value of optical modulator by means of the automatic bias control method; And

In step (c), near the direct current biasing that is determined described optical modulator in step (b) by described continuous wave light modulation.

5. according to claim 1 for controlling the method for optical transmitting set, further comprise:

The direct current biasing that the maximum of search and output from optical modulator and minimum value are corresponding; And

The direct current biasing of the orthogonal angles using the average voltage of described direct current biasing in controlling light modulation applies.

6. according to claim 1 for controlling the method for optical transmitting set, wherein,

In step (a), modulate the described continuous glistening light of waves by the data sequence with fixing, described fixed data sequence is selected as making

There is uniform amplitude according to the lightwave signal of described data sequence modulation in the center of the symbol of modulation, and

At least two continuous symbols of the lightwave signal of modulating according to described data sequence have the phase difference of 90 degree.

7. an optical transmitting set comprises:

Laser, described laser sends the continuous glistening light of waves;

Optical modulator, the described continuous glistening light of waves of described light modulator modulates;

Automatic bias control circuit, described automatic bias control circuit is controlled the magnitude of voltage of the direct current biasing of described optical modulator;

Encoder, described encoder is encoded and is exported multilevel signal the logic binary data; And

Driver, described driver amplifies described multilevel signal and drives thus described optical modulator;

The light amplitude of the described continuous glistening light of waves that wherein, will export from described optical modulator keeps constant;

Described automatic bias control circuit makes described magnitude of voltage converge to predetermined value; And

Described optical modulator utilizes a plurality of amplitude levels and phase level by described continuous wave light modulation to be near the magnitude of voltage of described convergence.

8. optical transmitting set according to claim 7, further comprise driver controller, described driver controller is measured and is started institute's elapsed time from nearest start-up time or the resetting time of described optical transmitting set, and connects described driver after described institute elapsed time has reached predetermined time;

9. optical transmitting set according to claim 7 further comprises:

Switch element, described switch element switches described driver; And

Control unit, described control unit is searched for the peaked direct current biasing corresponding to the output from described optical modulator, and orders the direct current biasing of described automatic bias control circuit orthogonal angles in controlling described optical modulator using the average voltage of described direct current biasing to apply.

10. optical transmitting set according to claim 7, further comprise recording controller, and described recording controller outputs to described encoder by the fixed data sequence;

Wherein, described fixing data sequence is selected as making

There is uniform amplitude according to the lightwave signal of described data sequence modulation in the center of the symbol of modulation, and

At least two continuous symbols of the lightwave signal of modulating according to described data sequence have the phase difference of 90 degree.

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